This invention relates generally to the field of turbochargers and, more particularly, to an air cooling system for controlling the temperature of an electric motor disposed within an electric assisted turbocharger.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of that shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
Because the rotary action of the turbine is dependent upon the heat and volumetric flow of exhaust gas exiting the engine, turbochargers are often of reduced effectiveness when the engine to which they are coupled is run at a low speed. The reduced effectiveness is often labeled turbo-lag. In order to overcome turbo-lag when the heat and volumetric flow of exhaust gas is low, turbochargers have been constructed that make use of an electric motor disposed therein to assist shaft rotation and to induce the compressor to spin.
The operating conditions found within an electric assisted turbocharger may produce temperatures high enough to cause motor overheating. Motor overheating may damage the stator of the electric motor, and may permanently de-magnetize the rotor of the electric motor. Additionally, electric assisted turbochargers are especially susceptible to entering compressor surge regimes, because such electric control of the compressor can enable the compressor to function in a manner that is relatively independent of engine operating conditions.
Generally speaking, compressor surge is a turbocharger condition whereby pressurized air created by the compressor meets an internal system resistance, oftentimes causing the pressurized air to be forced backwards through the turbocharger. Surge can occur from different turbocharger operating conditions, and is known to occur during engine operating conditions of deceleration. Compressor surge is generally an undesirable condition that can cause several problems from noise to component failure that can be detrimental to turbocharger and engine life and performance.
It is, therefore, desirable that an electric assisted turbocharger be constructed in a manner that minimizes potential electric motor problems due to high operating temperatures. It is also desired that such an electric assisted turbocharger be configured in a manner that minimizes and/or eliminates the a surge condition from occurring. It is desired that any such electric assisted turbocharger be constructed to provide such benefits in a manner that does not detrimentally impact desired turbocharger performance.
The present invention is for a system for controlling the temperature of an electric motor in an electric assisted turbocharger that is coupled to an internal combustion engine. The system has a turbocharger with an electric motor disposed within a motor housing. The motor housing has a motor housing airflow inlet and a motor housing airflow outlet. The turbocharger has a compressor with a compressor airflow inlet and a compressor airflow outlet. The turbocharger also has a turbine disposed within a turbine housing. Pressurized air taken downstream from the from the compressor outlet is routed to the motor housing airflow inlet for providing cooling air to the electric motor. Cooling air is removed from the electric motor via the motor housing airflow outlet, and is routed to the compressor inlet.
In an additional embodiment of the present invention, the system has a variable orifice fitting positioned adjacent the motor housing outlet for controlling an amount of air that passes through the motor housing outlet. A suitable actuator is coupled to the variable orifice fitting for operating the orifice. The system also has an electric motor controller electrically coupled to the electric motor and electrically coupled to the actuator. The electric motor controller controls the operation of the electric motor and the operation of the electric actuator, to both govern the speed of the electric motor and the amount of cooling air directed thereto for purposes of controlling electric motor temperature.
A motor temperature sensor is electrically coupled to the electric motor controller. The motor temperature sensor senses a temperature of the electric motor, and the electric motor controller controls the variable orifice fitting based upon signals received from the motor temperature sensor. Thus, the variable orifice fitting allows adequate cooling to prevent the motor from overheating, and also prevents too much air from being taken from the compressor output, which may have a negative impact on engine performance.
In an additional embodiment utilizing a variable orifice fitting and an electric actuator, an engine speed sensor is electrically coupled to the electric motor controller for sensing a rotational speed of the internal combustion engine. Additionally, a turbocharger speed sensor is coupled to the electric motor controller for sensing a rotation speed of the turbocharger shaft. A memory is electrically coupled to the electric motor controller. The memory has a multi-dimensional map stored therein of surge conditions correlating to the speed of the internal combustion engine and to the speed of the turbocharger. The electric motor controller is configured to control the electric actuator and the variable orifice fitting, based upon signals from the engine speed sensor and from the turbocharger speed sensor in view of the multi-dimensional map of surge conditions stored in the memory, in a manner avoiding surge.
In yet an additional embodiment utilizing a variable orifice fitting and an electronic actuator, an intake air sensor is electrically coupled to the electric motor controller. The intake air sensor senses a volume of air entering the turbocharger. A pressure ratio sensor is also electrically coupled to the electric motor controller. The pressure sensor senses a compressor pressure ratio. A memory is electrically coupled to the electric motor controller. The memory has a multi-dimensional map stored therein of surge conditions correlating to the speed of the internal combustion engine and to the speed of the turbocharger. The electric motor controller is configured to control the electronic actuator and the variable orifice fitting, based upon signals from the intake air sensor and from the pressure ratio sensor in view of the multi-dimensional map of surge conditions stored in the memory, in a manner avoiding surge.